/* This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * <p/>
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 */
package i3.swing.icon;

import java.awt.*;
import java.awt.image.*;
import java.io.*;
import java.util.*;

/**
 * Class GifDecoder - Decodes a GIF file into one or more frames. <br>
 *
 * <pre>
 *   Example:
 *      GifDecoder d = new GifDecoder();
 *      d.read(&quot;sample.gif&quot;);
 *      int n = d.getFrameCount();
 *      for (int i = 0; i &lt; n; i++) {
 *         BufferedImage frame = d.getFrame(i);  // frame i
 *         int t = d.getDelay(i);  // display duration of frame in milliseconds
 *         // do something with frame
 *      }
 * </pre>
 *
 * No copyright asserted on the source code of this class. May be used
 * for any purpose, however, refer to the Unisys LZW patent for any
 * additional restrictions. Please forward any corrections to
 * kweiner@fmsware.com.
 *
 * @author Kevin Weiner, FM Software; LZW decoder adapted from John
 *         Cristy's ImageMagick.
 * @version 1.03 November 2003
 */
@SuppressWarnings({"unchecked"})
class GifDecoder {

    /**
     * File read status: No errors.
     */
    public static final int STATUS_OK = 0;
    /**
     * File read status: Error decoding file (may be partially decoded)
     */
    public static final int STATUS_FORMAT_ERROR = 1;
    /**
     * File read status: Unable to open source.
     */
    public static final int STATUS_OPEN_ERROR = 2;
//    private BufferedInputStream in;
    private int status;
    private int width; // full image width
    private int height; // full image height
    private boolean gctFlag; // global color table used
    private int gctSize; // size of global color table
    private int loopCount = 1; // iterations; 0 = repeat forever
    private int[] gct; // global color table
    private int[] lct; // local color table
    private int[] act; // active color table
    private int bgIndex; // background color index
    private int bgColor; // background color
    private int lastBgColor; // previous bg color
    private boolean lctFlag; // local color table flag
    private boolean interlace; // interlace flag
    private int lctSize; // local color table size
    private int ix, iy, iw, ih; // current image rectangle
    private Rectangle lastRect; // last image rect
    private BufferedImage image; // current frame
    private BufferedImage lastImage; // previous frame
    private byte[] block = new byte[256]; // current data block
    private int blockSize = 0; // block size
    // last graphic control extension info
    private int dispose = 0;
    // 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev
    private int lastDispose = 0;
    private boolean transparency = false; // use transparent color
    private int delay = 0; // delay in milliseconds
    private int transIndex; // transparent color index
    private static final int MaxStackSize = 4096;
    // max decoder pixel stack size
    // LZW decoder working arrays
    private short[] prefix;
    private byte[] suffix;
    private byte[] pixelStack;
    private byte[] pixels;
    private ArrayList frames; // frames read from current file
    private int frameCount;

    private static class GifFrame {

        public GifFrame(BufferedImage im, int del) {
            image = im;
            delay = del;
        }
        public BufferedImage image;
        public int delay;
    }

    /**
     * Gets display duration for specified frame.
     *
     * @param n
     *            int index of frame
     * @return delay in milliseconds
     */
    public int getDelay(int n) {
        //
        delay = -1;
        if ((n >= 0) && (n < frameCount)) {
            delay = ((GifFrame) frames.get(n)).delay;
        }
        return delay;
    }

    /**
     * Gets the number of frames read from file.
     *
     * @return frame count
     */
    public int getFrameCount() {
        return frameCount;
    }

    /**
     * Gets the first (or only) image read.
     *
     * @return BufferedImage containing first frame, or null if none.
     */
    public BufferedImage getImage() {
        return getFrame(0);
    }

    /**
     * Gets the "Netscape" iteration count, if any. A count of 0 means
     * repeat indefinitiely.
     *
     * @return iteration count if one was specified, else 1.
     */
    public int getLoopCount() {
        return loopCount;
    }

    /**
     * Creates new frame image from current data (and previous frames as
     * specified by their disposition codes).
     */
    private void setPixels() {
        // expose destination image's pixels as int array
        int[] dest = ((DataBufferInt) image.getRaster().getDataBuffer()).getData();
        // fill in starting image contents based on last image's dispose
        // code
        if (lastDispose > 0) {
            if (lastDispose == 3) {
                // use image before last
                int n = frameCount - 2;
                if (n > 0) {
                    lastImage = getFrame(n - 1);
                } else {
                    lastImage = null;
                }
            }
            if (lastImage != null) {
                int[] prev = ((DataBufferInt) lastImage.getRaster().getDataBuffer()).getData();
                System.arraycopy(prev, 0, dest, 0, width * height);
                // copy pixels
                if (lastDispose == 2) {
                    // fill last image rect area with background color
                    Graphics2D g = image.createGraphics();
                    Color c = null;
                    if (transparency) {
                        c = new Color(0, 0, 0, 0); // assume background
                        // is transparent
                    } else {
                        c = new Color(lastBgColor); // use given
                        // background color
                    }
                    g.setColor(c);
                    g.setComposite(AlphaComposite.Src); // replace area
                    g.fill(lastRect);
                    g.dispose();
                }
            }
        }
        // copy each source line to the appropriate place in the
        // destination
        int pass = 1;
        int inc = 8;
        int iline = 0;
        for (int i = 0; i < ih; i++) {
            int line = i;
            if (interlace) {
                if (iline >= ih) {
                    pass++;
                    switch (pass) {
                        case 2:
                            iline = 4;
                            break;
                        case 3:
                            iline = 2;
                            inc = 4;
                            break;
                        case 4:
                            iline = 1;
                            inc = 2;
                    }
                }
                line = iline;
                iline += inc;
            }
            line += iy;
            if (line < height) {
                int k = line * width;
                int dx = k + ix; // start of line in dest
                int dlim = dx + iw; // end of dest line
                if ((k + width) < dlim) {
                    dlim = k + width; // past dest edge
                }
                int sx = i * iw; // start of line in source
                while (dx < dlim) {
                    // map color and insert in destination
                    int index = pixels[sx++] & 0xff;
                    int c = act[index];
                    if (c != 0) {
                        dest[dx] = c;
                    }
                    dx++;
                }
            }
        }
    }

    /**
     * Gets the image contents of frame n.
     *
     * @return BufferedImage representation of frame, or null if n is
     *         invalid.
     */
    public BufferedImage getFrame(int n) {
        BufferedImage im = null;
        if ((n >= 0) && (n < frameCount)) {
            im = ((GifFrame) frames.get(n)).image;
        }
        return im;
    }

    /**
     * Gets image size.
     *
     * @return GIF image dimensions
     */
    public Dimension getFrameSize() {
        return new Dimension(width, height);
    }

    /**
     * Reads GIF image from stream
     *
     * @param is InputStream
     *            containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(InputStream is) {
        init();
        if (is != null) {
            try {
                if (!(is instanceof BufferedInputStream)) {
                    is = new BufferedInputStream(is);
                }
                readHeader((BufferedInputStream) is);
                if (!err()) {
                    readContents((BufferedInputStream) is);
                    if (frameCount < 0) {
                        status = STATUS_FORMAT_ERROR;
                    }
                }
            } finally {
                try {
                    is.close();
                } catch (IOException ex) {
                    status = STATUS_OPEN_ERROR;
                }
            }
        } else {
            status = STATUS_OPEN_ERROR;
        }
        return status;
    }

    /**
     * Decodes LZW image data into pixel array. Adapted from John
     * Cristy's ImageMagick.
     */
    private void decodeImageData(BufferedInputStream is) {
        int NullCode = -1;
        int npix = iw * ih;
        int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, count, i, datum, data_size, first, top, bi, pi;
        if ((pixels == null) || (pixels.length < npix)) {
            pixels = new byte[npix]; // allocate new pixel array
        }
        if (prefix == null) {
            prefix = new short[MaxStackSize];
        }
        if (suffix == null) {
            suffix = new byte[MaxStackSize];
        }
        if (pixelStack == null) {
            pixelStack = new byte[MaxStackSize + 1];
        }
        // Initialize GIF data stream decoder.
        data_size = readAux(is);
        clear = 1 << data_size;
        end_of_information = clear + 1;
        available = clear + 2;
        old_code = NullCode;
        code_size = data_size + 1;
        code_mask = (1 << code_size) - 1;
        for (code = 0; code < clear; code++) {
            prefix[code] = 0;
            suffix[code] = (byte) code;
        }
        // Decode GIF pixel stream.
        datum = bits = count = first = top = pi = bi = 0;
        for (i = 0; i < npix;) {
            if (top == 0) {
                if (bits < code_size) {
                    // Load bytes until there are enough bits for a
                    // code.
                    if (count == 0) {
                        // Read a new data block.
                        count = readBlock(is);
                        if (count <= 0) {
                            break;
                        }
                        bi = 0;
                    }
                    datum += (block[bi] & 0xff) << bits;
                    bits += 8;
                    bi++;
                    count--;
                    continue;
                }
                // Get the next code.
                code = datum & code_mask;
                datum >>= code_size;
                bits -= code_size;
                // Interpret the code
                if ((code > available) || (code == end_of_information)) {
                    break;
                }
                if (code == clear) {
                    // Reset decoder.
                    code_size = data_size + 1;
                    code_mask = (1 << code_size) - 1;
                    available = clear + 2;
                    old_code = NullCode;
                    continue;
                }
                if (old_code == NullCode) {
                    pixelStack[top++] = suffix[code];
                    old_code = code;
                    first = code;
                    continue;
                }
                in_code = code;
                if (code == available) {
                    pixelStack[top++] = (byte) first;
                    code = old_code;
                }
                while (code > clear) {
                    pixelStack[top++] = suffix[code];
                    code = prefix[code];
                }
                first = suffix[code] & 0xff;
                // Add a new string to the string table,
                if (available >= MaxStackSize) {
                    break;
                }
                pixelStack[top++] = (byte) first;
                prefix[available] = (short) old_code;
                suffix[available] = (byte) first;
                available++;
                if (((available & code_mask) == 0)
                        && (available < MaxStackSize)) {
                    code_size++;
                    code_mask += available;
                }
                old_code = in_code;
            }
            // Pop a pixel off the pixel stack.
            top--;
            pixels[pi++] = pixelStack[top];
            i++;
        }
        for (i = pi; i < npix; i++) {
            pixels[i] = 0; // clear missing pixels
        }
    }

    /**
     * Returns true if an error was encountered during reading/decoding
     */
    private boolean err() {
        return status != STATUS_OK;
    }

    /**
     * Initializes or re-initializes reader
     */
    private void init() {
        status = STATUS_OK;
        frameCount = 0;
        frames = new ArrayList();
        gct = null;
        lct = null;
    }

    /**
     * Reads a single byte from the input stream.
     */
    private int readAux(BufferedInputStream is) {
        int curByte = 0;
        try {
            curByte = is.read();
        } catch (IOException e) {
            status = STATUS_FORMAT_ERROR;
        }
        return curByte;
    }

    /**
     * Reads next variable length block from input.
     *
     * @return number of bytes stored in "buffer"
     */
    private int readBlock(BufferedInputStream in) {
        blockSize = readAux(in);
        int n = 0;
        if (blockSize > 0) {
            try {
                int count = 0;
                while (n < blockSize) {
                    count = in.read(block, n, blockSize - n);
                    if (count == -1) {
                        break;
                    }
                    n += count;
                }
            } catch (IOException e) {
            }
            if (n < blockSize) {
                status = STATUS_FORMAT_ERROR;
            }
        }
        return n;
    }

    /**
     * Reads color table as 256 RGB integer values
     *
     * @param ncolors
     *            int number of colors to read
     * @return int array containing 256 colors (packed ARGB with full
     *         alpha)
     */
    private int[] readColorTable(int ncolors, BufferedInputStream in) {
        int nbytes = 3 * ncolors;
        int[] tab = null;
        byte[] c = new byte[nbytes];
        int n = 0;
        try {
            n = in.read(c);
        } catch (IOException e) {
        }
        if (n < nbytes) {
            status = STATUS_FORMAT_ERROR;
        } else {
            tab = new int[256]; // max size to avoid bounds checks
            int i = 0;
            int j = 0;
            while (i < ncolors) {
                int r = c[j++] & 0xff;
                int g = c[j++] & 0xff;
                int b = c[j++] & 0xff;
                tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
            }
        }
        return tab;
    }

    /**
     * Main file parser. Reads GIF content blocks.
     */
    private void readContents(BufferedInputStream is) {
        // read GIF file content blocks
        boolean done = false;
        while (!(done || err())) {
            int code = readAux(is);
            switch (code) {
                case 0x2C: // image separator
                    readImage(is);
                    break;
                case 0x21: // extension
                    code = readAux(is);
                    switch (code) {
                        case 0xf9: // graphics control extension
                            readGraphicControlExt(is);
                            break;
                        case 0xff: // application extension
                            readBlock(is);
                            StringBuilder app = new StringBuilder();
                            for (int i = 0; i < 11; i++) {
                                app.append((char) block[i]);
                            }
                            if ("NETSCAPE2.0".contentEquals(app)) {
                                readNetscapeExt(is);
                            } else {
                                skip(is); // don't care
                            }
                            break;
                        default: // uninteresting extension
                            skip(is);
                    }
                    break;
                case 0x3b: // terminator
                    done = true;
                    break;
                case 0x00: // bad byte, but keep going and see what happens
                    break;
                default:
                    status = STATUS_FORMAT_ERROR;
            }
        }
    }

    /**
     * Reads Graphics Control Extension values
     */
    private void readGraphicControlExt(BufferedInputStream is) {
        readAux(is); // block size
        int packed = readAux(is); // packed fields
        dispose = (packed & 0x1c) >> 2; // disposal method
        if (dispose == 0) {
            dispose = 1; // elect to keep old image if discretionary
        }
        transparency = (packed & 1) != 0;
        delay = readShort(is) * 10; // delay in milliseconds
        transIndex = readAux(is); // transparent color index
        readAux(is); // block terminator
    }

    /**
     * Reads GIF file header information.
     */
    private void readHeader(BufferedInputStream is) {
        StringBuilder id = new StringBuilder();
        for (int i = 0; i < 6; i++) {
            id.append((char) readAux(is));
        }
        if (!id.toString().startsWith("GIF")) {
            status = STATUS_FORMAT_ERROR;
            return;
        }
        readLSD(is);
        if (gctFlag && !err()) {
            gct = readColorTable(gctSize, is);
            bgColor = gct[bgIndex];
        }
    }

    /**
     * Reads next frame image
     */
    private void readImage(BufferedInputStream is) {
        ix = readShort(is); // (sub)image position & size
        iy = readShort(is);
        iw = readShort(is);
        ih = readShort(is);
        int packed = readAux(is);
        lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
        interlace = (packed & 0x40) != 0; // 2 - interlace flag
        // 3 - sort flag
        // 4-5 - reserved
        lctSize = 2 << (packed & 7); // 6-8 - local color table size
        if (lctFlag) {
            lct = readColorTable(lctSize, is); // read table
            act = lct; // make local table active
        } else {
            act = gct; // make global table active
            if (bgIndex == transIndex) {
                bgColor = 0;
            }
        }
        int save = 0;
        if (transparency) {
            save = act[transIndex];
            act[transIndex] = 0; // set transparent color if
            // specified
        }
        if (act == null) {
            status = STATUS_FORMAT_ERROR; // no color table defined
        }
        if (err()) {
            return;
        }
        decodeImageData(is); // decode pixel data
        skip(is);
        if (err()) {
            return;
        }
        frameCount++;
        // create new image to receive frame data
        image = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_ARGB_PRE);
        setPixels(); // transfer pixel data to image
        frames.add(new GifFrame(image, delay)); // add image to frame
        // list
        if (transparency) {
            act[transIndex] = save;
        }
        resetFrame();
    }

    /**
     * Reads Logical Screen Descriptor
     */
    private void readLSD(BufferedInputStream is) {
        // logical screen size
        width = readShort(is);
        height = readShort(is);
        // packed fields
        int packed = readAux(is);
        gctFlag = (packed & 0x80) != 0; // 1 : global color table flag
        // 2-4 : color resolution
        // 5 : gct sort flag
        gctSize = 2 << (packed & 7); // 6-8 : gct size
        bgIndex = readAux(is); // background color index
        readAux(is); // pixel aspect ratio
    }

    /**
     * Reads Netscape extenstion to obtain iteration count
     */
    private void readNetscapeExt(BufferedInputStream is) {
        do {
            readBlock(is);
            if (block[0] == 1) {
                // loop count sub-block
                int b1 = block[1] & 0xff;
                int b2 = block[2] & 0xff;
                loopCount = (b2 << 8) | b1;
            }
        } while ((blockSize > 0) && !err());
    }

    /**
     * Reads next 16-bit value, LSB first
     */
    private int readShort(BufferedInputStream is) {
        // read 16-bit value, LSB first
        return readAux(is) | (readAux(is) << 8);
    }

    /**
     * Resets frame state for reading next image.
     */
    private void resetFrame() {
        lastDispose = dispose;
        lastRect = new Rectangle(ix, iy, iw, ih);
        lastImage = image;
        lastBgColor = bgColor;
        dispose = 0;//was local
        transparency = false;//was local
        delay = 0;//was local
        lct = null;
    }

    /**
     * Skips variable length blocks up to and including next zero length
     * block.
     */
    private void skip(BufferedInputStream is) {
        do {
            readBlock(is);
        } while ((blockSize > 0) && !err());
    }
}
